Conventionally, formed articles made of heat resistant polymers have been used in an electrical insulation field where heat resistance is required. Especially, formed articles using aromatic polyamides (hereinafter, referred to as aramids) are excellent industrial materials having heat resistance, chemical resistance, and flame retardancy attributable to the molecular structures of the aramids. In particular, a paper (product name: KOMEX (registered trademark)), made of a fibrid and a fiber of poly (meta-phenylene isophthalamide) has been widely used as an electrically insulating paper excellent in heat resistance.
Likewise, laminates in which any of the above-described formed articles and a sheet material having different material properties, such as a resin film, are laminated on each other have been used in the electrically insulating applications. The stacking of the sheet materials having different material properties in such a laminate makes it possible to make use of characteristics of both the sheet, materials as characteristics of the laminate.
Methods for producing such a laminate include a method in which the laminate is obtained by applying an adhesive agent based on urethane, acrylic, or the like onto a mating surface between a heat resistant sheet material and a resin film, and thus laminating the sheet material and the resin film on each other (for example, Patent Literature 1), a method in which a molten resin composition is applied onto a heat resistant sheet material by a method such as extrusion, and thus a sheet layer of the resin composition is formed (for example, Patent Literature 2), and the like.
However, the former method has such a problem that the insulating performance is affected by degradation of the adhesive agent in the applications where the laminate is exposed to a high-temperature atmosphere for a long period, because the heat resistance of the adhesive agent is inferior to those of the heat-resistant sheet material and the resin film. The latter method is free from this problem, because no adhesive agent is used. However, the latter method has such a problem that the laminate has lower mechanical strength than a laminate in which a highly drawn resin film is laminated, because the resin composition in a molten state is applied, i.e., because the resin composition takes a so-called undrawn or slightly drawn state.